-LRB- CNN -RRB- -- More than 2,000 lives lost . A vast and unfolding humanitarian crisis . And the downing of a civilian airliner that shocked the world .

It 's hard to imagine -- but true -- that the raging conflict between Ukraine and Russia , or at least Ukraine and pro-Russian rebels , all started with a humble trade agreement .

As tensions run high over a Russian aid convoy described by Western leaders as a provocative incursion , reports of direct Russian military activity inside Ukraine and Ukrainian fears of an outright invasion , it 's time to look back on how we got here , and where things are headed :

How it started

While the roots of the crisis run quite deep , what 's happening now began to unfold in earnest in the fall of 2013 .

That 's when then-Ukrainian President Viktor Yanukovych scuttled a trade deal with the European Union that would have pulled the country , so recently a satellite of the Soviet Union , toward Europe in the latest twirl of a dance that has lasted centuries .

Instead , Yanukovych jumped at Russian President Vladimir Putin 's offer to buy $ 15 billion in debt from his cash-strapped government and cut the price of vital natural gas to the country .

Yanukovych 's decision set off protests in Ukraine 's more Europe-leaning west calling for the government 's ouster . Security forces responded harshly , beating protesters and firing live ammunition into demonstrations , resulting in several deaths . As clashes spread , so did international anger over the situation .

By late February , Yanukovych had fled to Russia , the government had fallen and a new pro-Europe government had formed to replace it .

That , in turn , set off pro-Russian demonstrations in Crimea , a semi-autonomous Ukrainian republic and the location of a major Russian navy base .

After thousands of Russian troops filtered into the territory -- purportedly at the invitation of Ukraine 's self-exiled president -- Ukraine 's regional parliament called a referendum on secession , and before you could say `` borscht , '' Crimea was part of Russia .

And it 's here that things turned even uglier . Pro-Russian fighters occupied government buildings in the country 's east , demanding a referendum on independence .

Before long , rebel forces -- believed to be supported by Russia -- had taken control of major cities in Ukraine 's east . Fighting broke out between the rebel groups and Ukraine 's military , fighting that continues today .

In a major and likely inadvertent escalation in July , a suspected surface-to-air missile believed to have been operated by pro-Russian rebels shot down Malaysia Airlines Flight 17 , killing all 298 people aboard and hardening Western opinion , particularly in Europe , against Russia .

What 's happening now

Ukraine 's military has been on the offensive recently against the pro-Russian forces , but those successes seem to have slowed .

Russian troops remain camped along the Ukrainian border , Western leaders say .

And Ukrainian officials said Tuesday that they had detained 10 Russian soldiers in the Donetsk region of eastern Ukraine , further evidence , Kiev says , of direct Russian involvement in the conflict .

Meanwhile , the United Nations has warned of a growing humanitarian crisis sure only to get worse unless something is done to stem the fighting .

What 's next

A full-scale invasion is unlikely . While Putin 's approval rating among Russians is sky-high , recent polling shows the Russian people are n't wild about an out-and-out invasion of Ukraine , said Robert D. Kaplan , the chief geopolitical analyst for Stratfor . `` He may be a dictator , but dictators care about public opinion as much as democrats , '' he said .

But any talk of peace from Putin is likely a stalling tactic . Putin is buying time so that he can continue slipping arms and aid to help rebels recover from their recent losses , said Heather Conley , senior vice president of Europe and Eurasia at the Center for Strategic and International Studies . `` His best option is to have a permanent frozen conflict , '' she said .

Fall and winter will slow the fighting . Kaplan said the colder seasons in Ukraine mean mud and mud means a slower tempo for military operations . Just do n't expect total silence , he says -- there will still be fighting .

Moscow will try to squeeze Ukraine . Putin will slow the flow of crucial natural gas and goods into Ukraine , putting further pressure on Kiev 's economy and war-fighting ability . `` The Russians will try everything to weaken the regime in Kiev , '' Kaplan said .

The West has some soul-searching to do . Sanctions applied by the United States and Europe against Russia have so far only played into Putin 's playbook , enhancing the image of an aggrieved Russia trying to shake off its detractors , Conley said . Putin 's strategy of assembling a larger Russian empire has significant ramifications for Estonia and Latvia , Conley said , raising questions about just what the West will do to stop Russia if Putin chooses to further extend his reach .

And what will it take to end this ? Ukraine is a linchpin of Putin 's plans for Russia , whether it 's reassembling a historical empire or shoring up the Russian economy , Conley says . So whatever happens must support that . Kaplan says Putin ca n't pull back without gaining assurances that Ukraine will never become part of NATO . Ukraine , he said , needs assurances about its sovereignty and energy security .

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The Ukraine conflict started with a dispute over a trade deal

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That ballooned into protests , then Russia stepped in

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Looking forward , an outright invasion seems unlikely , analysts say

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It wo n't be easy to unravel the complex political and economic forces tugging at Ukraine